1. Field of the Invention
The present invention relates generally to transferring wafers among modules of semiconductor processing equipment, and more particularly to a module having a controllable mini-environment.
2. Description of the Related Art
In the manufacture of semiconductor devices, process chambers are interfaced to permit transfer of wafers or substrates, for example, between the interfaced chambers. Such transfer is via transport modules that move the wafers, for example, through slots or ports that are provided in the adjacent walls of the interfaced chambers. For example, transport modules are generally used in conjunction with a variety of substrate processing modules, which may include semiconductor etching systems, material deposition systems, and flat panel display etching systems. Due to the growing demands for cleanliness and high processing precision, there has been a growing need to reduce the amount of human interaction during and between processing steps. This need has been partially met with the implementation of vacuum transport modules which operate as an intermediate handling apparatus (typically maintained at a reduced pressure, e.g., vacuum conditions). By way of example, a vacuum transport module may be physically located between one or more clean room storage facilities where substrates are stored, and multiple substrate processing modules where the substrates are actually processed, e.g., etched or have deposition performed thereon. In this manner, when a substrate is required for processing, a robot arm located within the transport module may be employed to retrieve a selected substrate from a load lock chamber and place it into one of the multiple processing modules.
As is well known to those skilled in the art, the arrangement of transport modules to xe2x80x9ctransportxe2x80x9d substrates among multiple storage facilities and processing modules is frequently referred to as a xe2x80x9ccluster tool architecturexe2x80x9d system. FIG. 1A depicts a typical semiconductor process cluster architecture 100 illustrating the various chambers that interface with a vacuum transport module 106. Vacuum transport module 106 is shown coupled to three processing modules 108a-108c which may be individually optimized to perform various fabrication processes. By way of example, processing modules 108a-108c may be implemented to perform transformer coupled plasma (TCP) substrate etching, layer depositions, and/or sputtering.
Connected to vacuum transport module 106 is a load lock 104 that may be implemented to introduce substrates into vacuum transport module 106. The load lock 104 can be coupled to an atmospheric transport module (ATM) 103 that interfaces with the clean room 102. The ATM 103 typically has region for holding cassettes of wafers and a robot that retrieves the wafers form the cassettes and moves them into and out of the load lock 104. As is well known, the load lock 104 serves as a pressure-varying interface between vacuum transport module 106 and the ATM 103. Therefore, vacuum transport module 106 may be kept at a constant pressure (e.g., vacuum), while the ATM 103 and clean room 102 are kept at atmospheric pressure.
FIG. 1B illustrates a partial system diagram 150 including an atmospheric transport module (ATM) 103 which includes a filter/blower 152a, a robot 156 having an arm set 158, and a shelf 154. The shelf 154 is configured to hold a cassette 160 of wafers 162 within a cassette environment 152b. The cassette environment 152b of the ATM 103 has a door 155 which can be opened to insert or remove the cassette 160 during processing. The filter/blower 152a is configured to generate an air flow 170 in the ATM 103 and thus, cause the air flow substantially undisturbed through a particle screen 171 to a lower portion of the ATM 103 and then out an exhaust vent 152c. In addition, the ATM 103 is simplistically shown connected to the load lock 104 and to the transport module 106. As mentioned above, the transport module 106 can then transfer wafers between selected processing modules 108.
Although this type of prior art ATM 103 is capable of transferring wafers from the cassette 160 into and out of the load lock 104 quite efficiently, the air flow 170 has been observed to bypass the cassette environment 152b during the operation of the blower 152a. As a result, the cassette environment 152b remains substantially static. That is, the environment between the wafers 162 remains substantially unaffected by the air flow 170 during operation.
FIG. 1C illustrates a more detailed view of the cassette 160 having a plurality of wafers 162. In general, after a wafer has been processed in one of the processing modules 108 and stacked back into the cassette 160, post-process gasses will typically hover between the respective wafers 162. The gasses are pictorially illustrated by 166 emanating from the top surfaces of recently processed wafers 162. A problem with having such gasses 166 between the wafers 162 is that the chemical gasses can, in some cases, continue to chemically react and cause degradation in the yield of the processed wafers 162. If wafers are degraded sufficiently, the potential financial loss associated with reduced yields can be significant.
Another problem with having a stagnant cassette environment 152b is that any particles that may have fallen onto the surfaces of the wafers 162 will continue to remain on the top surfaces of the wafer while the cassette rests in the cassette environment 152b. These particles 164, in some cases can cause substantial damage to the semiconductor circuits formed on the wafers 162. It is well known that it is undesirable to allow particles 164 to remain on the surface of the wafers 162 in between the processing operations. The longer the particles remain on the surface of the wafers 162, the higher the probability that such particles will cause damage to sensitive integrated circuitry, and will be harder to clean.
Still another problem with having cassettes 160 sit in static environment 152b is that once a process engineer opens door 155 to remove the cassette 160, the cassette 160 may expose the process engineer to potentially undesirable levels of toxic gasses 166 that emanate from the surfaces of the wafers 162. In some cases, such exposure to process gasses and chemical by-products can cause process engineers handling such cassettes to become disoriented and thus potentially drop the cassette 160 full of valuable processed semiconductor wafers 162.
In view of the foregoing, what is needed is an atmospheric transport module that is capable of controlling the environment in and around a cassette of wafers.
Broadly speaking, the present invention fills these needs by providing an atmospheric transport module capable of generating a mini-environment in a region where cassettes of wafers are temporarily stored during processing. The mini-environment is preferably configured to define an air flow through the wafers such that process gases and by-products are substantially purged away from the environment surrounding the wafers. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, an atmospheric transport module is disclosed. The module has a housing and the housing includes a number of inventive elements. The housing has a top portion that contains a blower for generating a regulated air flow in a downward direction that is away from the top portion of the housing. A load cell region is also included and it is laterally offset from the blower. The load cell includes a shelf for supporting a wafer cassette and the shelf is separated from a wall of the load cell to thus define a redirection air flow slot. A perforated sheet is defined below the blower, and the perforated sheet is configured to restrict air flow through the perforated sheet and induce a redirected air flow through the wafer cassette that sits on the laterally offset load cell. An advantage of the redirected air flow is that residual process gasses that may be hovering over the wafers in the wafer cassette are pushed away from the wafer cassette and down the redirection air flow slot. Another advantage is that when the doors are opened, air will flow out, reducing the chance that particles from outside will move in.
In another embodiment, an atmospheric transport module is disclosed. The module includes an enclosed housing having a top region, a central region, a bottom region, and a load cell region. A blower is located in the top region of the enclosed housing and is configured to generate a flow of air downward into the central region. A shelf in the load cell region defines a separation between the central region and the bottom region of the enclosed housing. The shelf is at least partially spaced apart from a wall of the load cell region to thereby define a slot behind the shelf. A perforated sheet is configured to extend from the shelf and further define the separation between the central region and the bottom region. In this embodiment, air flow generated by the blower is restricted from freely flowing through the perforated sheet and is partially caused to be redirected toward the shelf of the load cell, through the slot and into the bottom region of the enclosure housing.
Once the redirected air flow and the non-redirected air flow (flowing through the perforated sheet) enters the bottom region, the air is channeled out through a vent. In an alternative embodiment, a fan can be installed in the bottom region to assist the redirected air flow through the slot that is defined behind the shelf. In this manner, when a cassette having one or more wafers sits on the shelf in the load cell region, the redirected air flow will be caused to circulate any post-process gases and particles that may be present over the wafers. The post-process gases and any particles are thus caused to flow out to the bottom region of the enclosed housing and out the vent. In this embodiment, the fan is preferably interlocked to the door(s) of the load cell so that the fan switches off when any one of the doors of the load cell is opened. In this manner, dirty air is not pulled into the ATM by the fan when the door opens, thus contaminating the wafers.
In yet another embodiment, a method of making an atmospheric transport module is disclosed. The method includes forming an enclosed housing having a top region, a central region, a bottom region, and a load cell region. A blower is installed in the top region of the enclosed housing, and the blower is configured to generate a flow of air downward into the central region. A shelf is installed in the load cell region and the shelf defines a separation between the central region and the bottom region of the enclosed housing. The shelf is at least partially spaced apart from a wall of the load cell region and thereby defines a slot behind the shelf. A perforated sheet is installed in a manner that extends horizontally from the shelf and further defines the separation between the central region and the bottom region. The air flow generated by the blower is restricted from freely flowing through the perforated sheet and is partially caused to be redirected away from the perforated sheet and toward the shelf of the load cell, through the slot and into the bottom region of the enclosure housing.
A wafer cassette having one or more wafers is configured to sit on the shelf of the load cell and thus receive the redirected air flow. The redirected air flow therefore keeps a gentle flow of air flowing over any wafers that may be temporarily stored in the wafer cassette. The shelf can be configured to hold more than one wafer cassette, and an isolating enclosure can be built around each wafer cassette to maintain a stable mini-environment when a door behind the shelf is opened to access a particular one of the wafer cassettes.
Advantageously, the gentle flow of redirected air over the wafers ensures that wafers sitting in the load cell are not sitting in a static environment and thus cause the build up of post-process gases. The gentle flow of redirected air also assists in removing microscopic particles from over the wafers sitting in the cassettes, thus maintaining a controlled mini-environment that fosters higher yields and higher quality processed wafers. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.